To send content items to your account,
please confirm that you agree to abide by our usage policies.
If this is the first time you use this feature, you will be asked to authorise Cambridge Core to connect with your account.
Find out more about sending content to .
To send content items to your Kindle, first ensure firstname.lastname@example.org
is added to your Approved Personal Document E-mail List under your Personal Document Settings
on the Manage Your Content and Devices page of your Amazon account. Then enter the ‘name’ part
of your Kindle email address below.
Find out more about sending to your Kindle.
Note you can select to send to either the @free.kindle.com or @kindle.com variations.
‘@free.kindle.com’ emails are free but can only be sent to your device when it is connected to wi-fi.
‘@kindle.com’ emails can be delivered even when you are not connected to wi-fi, but note that service fees apply.
In response to the ‘oldest ice’ challenge initiated by the International Partnerships in Ice Core Sciences (IPICS), new rapid-access drilling technologies through glacier ice need to be developed. These will provide the information needed to qualify potential sites on the Antarctic ice sheet where the deepest section could include ice that is >1Ma old and still in good stratigraphic order. Identifying a suitable site will be a prerequisite for deploying a multi-year deep ice-core drilling operation to elucidate the cause and mechanisms of the mid-Pleistocene transition from 40 ka glacial–interglacial cycles to 100 ka cycles. As part of the ICE&LASERS/SUBGLACIOR projects, we have designed an innovative probe, SUBGLACIOR, with the aim of perforating the ice sheet down to the bedrock in a single season and continuously measuring in situ the isotopic composition of the melted water and the methane concentration in trapped gases. Here we present the general concept of the probe, as well as the various technological solutions that we have favored so far to reach this goal.
We report the observation of T Tau by visible speckle interferometry at the CFHT. The observations were carried out at two wavelengths simultaneously. Each image was split into two, allowing improved data processing. The 4-channel photon-counting detector CP40 was used. We have discovered that 30% of the total energy at Hα is emitted by an extended elliptical component, with a FWHM of 70 marcsec. In the neighbouring continuum, T Tau is not resolved by the 3.60 m CFHT. We briefly discuss the astrophysical consequences of this new result.
A technique for reconstructing diffraction-limited image of an object from speckle images without reference star is applied to both simulated and real data. The object spectrum is estimated by blind deconvolution using the power spectrum of the speckle images and the phase is restored from the bispectrum.
This tutorial paper describes the problem of image reconstruction from interferometric data with a particular focus on the specific problems encountered at optical (visible/IR) wavelengths. The challenging issues in image reconstruction from interferometric data are introduced in the context of a general inverse problem approach. This framework is then used to describe state-of-the-art image reconstruction algorithms specifically developed for optical interferometry.
The close environment of Herbig stars starts to be revealed step by step and it appears to be quite complex. Many physical phenomena interplay: the dust sublimation causing a puffed-up inner rim, a dusty halo, a dusty wind or an inner gaseous component. To investigate more deeply these regions, getting images at the first Astronomical Unit scale is necessary. This has become possible with near infrared instruments on the VLTI. We have developed a new imaging method adapted to young stellar objects where we process separately the stellar component from the rest of the image to reveal the environment by using the spectral differences between these two components. We present the result of this method on the first imaging survey of Herbig stars carried out by PIONIER on the VLTI.
Zinc oxide (ZnO) nanoparticles and nanoparticles of luminescent zinc oxide (ZnO:Zn) phosphor were successfully synthesised and well characterised. A transparent polystyrene composite sheet containing ZnO:Zn nanoparticles was prepared by a solvent casting method. The sheet manifested comparable transmission to a virgin polystyrene film due to very uniform dispersion of the ZnO:Zn nanoparticles into the polystyrene. Evidence for uniform dispersion was evident in both its luminescent properties and in a SEM image. The photoluminescent characteristics of the ZnO:Zn, both as a pure powder and embedded in a polystyrene matrix, are reported. The uniformity of the photoluminescence of the composite sheet under near ultraviolet excitation is demonstrated. The luminescent ZnO:Zn nanoparticles are shown to have applications for use not only as an inhibitor of the ultraviolet degradation of polymers, but also for providing polymers with light emitting functionality.
Image reconstruction from interferometric data is an inverse problem. Owing to the sparse spatial frequency coverage of the data and to missing Fourier phase information, one has to take into account not only the data but also prior constraints. Image reconstruction then amounts to minimizing a joint criterion which is the sum of a likelihood term to enforce fidelity to the data and a regularization term to impose the priors. To implement strict constraints such as normalization and non-negativity, the minimization is performed on a feasible set. When the complex visibilities are available, image reconstruction is relatively easy as the joint criterion is convex and finding the solution is similar to a deconvolution problem. In optical interferometry, only the powerspectrum and the bispectrum can be measured and the joint criterion is highly multi-modal. The success of an image reconstruction algorithm then depends on the choice of the priors and on the ability of the optimization strategy to find a good solution among all the local minima.
In this paper we present a method for hyper-spectral image restoration for integral field spectrographs (IFS) data. We specifically address two topics: (i) the design of a fast approximation of spectrally varying operators and (ii) the comparison between two kind of regularization functions: quadratic and spatial sparsity functions. We illustrate this method with simulations coming from the Multi Unit Spectroscopic Explorer (MUSE) instrument. It shows the clear increase of the spatial resolution provided by our method as well as its denoising capability.
For many years TREFLE, The Ecully team treating labio-palatal clefts, has begun managing the care of patients with clefts at younger and younger ages. Both surgically and orthodontically we design our therapeutic interventions to change the environment of the cleft as rapidly as possible in order to improve patients’ functioning that will in turn have a beneficial effect on growth and esthetics. We have found that our patients treated in this way not only have improved appearance but also less likelihood of needing orthognathic surgery. We have also found that our patients do not routinely require early bone grafts, at about 6 years of age. We determine which children will require this intervention in a re-evaluation that we undertake after the completion of the primary phase of orthopedic and orthodontic therapy.
To make our technique as clear as possible throughout the course of this article we present the different stages of treatment of four children, Leslie, Jules, Nathan, and Élodie.
The oceanic forced wave beneath a moving atmospheric disturbance is amplified by Proudman resonance. When modified by the Earth's rotation this classical resonance only occurs if the disturbance time scale is smaller than the inertial period. With or without Coriolis effects, free transients generated by storm forced waves obliquely crossing step changes in water depth at particular angles are shown to resonate by exciting a range of long barotropic free waves. Rotationally influenced slow atmospherically forced waves crossing a vertical coast at a critical angle lead to a form of subcritical resonance, which occurs only when the component of the disturbances' phase velocities along the coast matches that of a free Kelvin wave (KW). In a rotating ocean, transients generated by disturbances crossing a step at a particular angle are shown to excite a free double Kelvin wave (DKW). This new type of resonance only occurs for sufficiently large steps and disturbances with time scale greater than the inertial period. A storm crossing a step shelf can result in the excitation of an infinite set of edge waves, a single KW, a unique DKW and a first-mode continental shelf wave, depending on the topography and the disturbance time scale, translation speed and incident angle. The study of resonances and wave mode excitations generated by storms crossing a coast or a continental shelf may contribute to understanding how a particular combination of the storm characteristics can result in destructive coastal events with time scales encompassing the typical meteotsunami period band (tens of minutes) and storm surges with periods of several hours or days.
Using the modulated scatterer technique allows us to measure the electromagnetic field in an applicator. The design of a new sensor modulated at 25 Hz is described. The operating conditions and the performance are presented.
The sensor can be used for measuring high microwave electric fields up to 10 kV/m in an industrial applicator supplied by any industrial magnetron.
As a consequence of the BERGMAN - MILTON theory, which expresses the effective permittivity of a two phase mixture with an integral of a density function, it has been possible to evaluate the local electrical field strength inside a heterogeneous mixture. The developed formula can be used advantageously for modeling the local temperature inside a ceramic material during its microwave sintering.
The present study aimed at estimating the characteristics of the Ascophyllum nodosum stands along the coast of Brittany, France. Although both an ecologically and economically important macroalga on sheltered rocky shores of the North Atlantic, no study has simultaneously dealt with the variability of the densities, lengths and biomasses of A. nodosum together with a description of its associated algal and animal diversity. There were significant differences in mean lengths and variations in the length–population structures between sites. However, the biomasses and densities showed no significant differences. The biomasses are amongst the highest ones estimated over the entire species distribution. The algal and animal assemblages were typical of A. nodosum zones, but only the identity composition of the algal communities seemed to reflect site differences in environmental forces. The biomasses measured in the present study should help improve future macroalgae biomass and metabolism estimates on regional or global scales. Finally, the data will provide a reference state for future studies on the responses of fucoid canopies to environmental changes.
Images in visible interferometry are characterised by their low coherence time, and except for brightest stars, the flux on the detector is much less than one photon per pixel per image. Algol and Comptage de Photons Nouvelle Génération (CPNG) are new photon counting cameras developed for high angular resolution in the visible. They are intensified CCDs built to benefit from improvements in photonic commercial components, and personal computer processing power. We present how we achieve optimal performances (sensitivity and spatiotemporal resolution) by the combination of proper optical and electronics design, and real-time elaborated data processing. The number of pixels is 532 × 516 and 768 × 640 read at a frame rate of 262 Hz and 50 Hz for CPNG and Algol respectively. The dark current is very low: 5 × 10-4 electron.pixel-1.s-1. Quantum efficiencies reach up to 36% in the visible with the GaAsP photocathodes and and 26% in the red with the GaAs ones, thanks to the sensitivity of the photocathodes and to the photon centroiding algorithm; they are likely the highest values reported for ICCDs.
Deep-sea hydrothermal vents display extreme and highly variable environmental conditions that are expected to be among the most important factors structuring associated benthic populations and communities. We tested this assumption, focusing on the distribution of gastropods, as well as on the demographic population structure and reproductive biology of one dominant gastropod species in zones characterized by alvinellid polychaetes and vestimentiferan tubeworms. A total of 14 biological samples from both types of habitats were collected at three sites on the East Pacific Rise 13°N vent field in May 2002. At all vents except one, the physico-chemical environment was described in two steps: (1) pH, total sulphide and reduced iron concentrations have been measured in situ in Alvinella habitats and correlations to temperature were assessed at the scale of each sampled vent; and (2) assuming the consistency of these relationships within a single edifice, ranges of physico-chemical factors were estimated for each biological sample from the corresponding fine scale temperature measurements. A total of 11 gastropod species were identified from all samples and 2 main faunal assemblages were distinguished: one dominated by Lepetodrilus elevatus in the alvinellid zone as well as in the vestimentiferan zone, and one dominated by the peltospirids Nodopelta heminoda, N. subnoda and Peltospira operculata confined to the alvinellid zone. Peltospirid gastropods were dominant over lepetodrilid gastropods in the more acidic, sulphide-richer, and hotter environments. Although this pattern could be related to specific physiological tolerances to temperature and sulphide toxicity, the weak correlation between community structure and physico-chemical variables suggests that additional factors are also involved. Particularly, the low species richness and the overwhelming dominance of L. elevatus in one faunal assemblage suggest that this species may outcompete peltospirids and greatly affect community structure. This hypothesis is supported by large differences in the demographic structure and reproductive biology of L. elevatus between the 2 faunal assemblages.
This paper first gives an introduction to the broad features of the Darwin mission of ESA and
then describes in some detail the data processing that is necessary to detect planets and
spectrally characterize them. The proposed data processing method is
validated by means of simulated data.